The present invention pertains to a method for connecting a magnetic substance target with less variation in plate thickness to a backing plate, and to the magnetic substance target itself.
Conventionally, when performing magnetron sputtering to a ferromagnetic substance target such as iron, cobalt, nickel, platinum or the alloys thereof upon disposing a magnet to the back of such a target, the magnetic field inside the target was blocked, and it was difficult to generate a magnetic field on the target surface.
In other words, as a result of the magnetic field effect characteristic to ferromagnetic bodies such as iron, cobalt, nickel, platinum or the like, the plasma density did not rise, the ionization efficiency of argon deteriorated, and, as a result, the sputtering efficiency became deteriorated.
Thus, upon employing a ferromagnetic substance target such as iron, cobalt, nickel, platinum or the alloys thereof, measures were taken to generate a magnetic field leak by simply making the target thickness thin.
Generally, for the conventional connection of a magnetic substance target and a backing plate, a low-melting bonding material such as indium or the like was used.
Nevertheless, recently, this type of bonding material such as indium with weak bonding strength sometimes peels due to the influence of heat generated when latest high-power sputtering is employed. Thus, diffusion bonding has been proposed instead of this kind of bonding material, and, today, this diffusion bonding is becoming mainstream.
In light of the above, this is no exception to targets such as iron, cobalt, nickel, platinum and the alloys thereof, and diffusion bonding is similarly being performed thereto.
Meanwhile, although aluminum or aluminum alloy is generally used as the backing plate, when using such aluminum or aluminum alloy, the difference in the coefficient of thermal expansion between iron, cobalt, nickel, platinum or the alloys thereof and the aluminum or aluminum alloy will become significant, and, as a result, there were cases where the bonding interface would peel due to the increase in the cambering amount during the cooling process after diffusion.
In recent years, sputtering particles are being ionized with further high-power sputtering so as to perform even deposition while providing high kinetic energy to the substrate. As a result, the target to which the backing plate is connected deforms significantly in a convex shape due to the thermal influence during sputtering and the water pressure of the cooling medium, and there were cases where water leakage would occur.
Recently, the target itself is being enlarged pursuant to the enlargement of the bore diameter of wafers, and the peeling of the bonding interface and the deformation of the backing plate are becoming major problems. In consideration of the above, copper and copper alloy having stronger strength are being used as the backing plate.
Incidentally, with the ferromagnetic substance targets formed from iron, cobalt, nickel, platinum or the alloys thereof as described above, in order to provide anisotropy to magnetism of the ferromagnetic substance target, complete annealing will not be performed thereto after final plastic working, and it is necessary to leave in the as-wrought structure the processing stress caused by the plastic working.
Although it is one characteristic of a ferromagnetic substance target to have such remnant stress, a major problem here is in that the remnant stress may cause cambering in the ferromagnetic substance target material such as iron, cobalt, nickel, platinum or the alloys thereof during the bonding process to the backing plate. For instance, although heat of roughly 200 to 250° C. will be applied during the bonding process, cambering will occur even with the application of heat at such lower temperatures.
In order to improve the sputtering efficiency of the magnetron sputtering target as described above, a target material having a thickness of 10 mm or less, generally 5 mm or less is formed, but cambering appears notably with such a thin target, and there is a problem in that this is extremely difficult to restore.
Generally, a ferromagnetic substance target formed from iron, cobalt, nickel, platinum or the alloys thereof is ultimately retained in a vacuum chuck and subject to grinding. Even if the flatness thereof is maintained during the retention in such chuck, if cambering occurs even once, a phenomenon of re-cambering may occur after the release of the chuck.
As described above, since a target material is thin, the problem of cambering is serious, and there is a problem in that such target material cannot be easily connected to the backing plate while maintaining the flatness thereof.